U.S. Pat. No. 6,439,188; the disclosure of which is incorporated herein by reference in entirety, discloses a four-cycle, four-cylinder, in-line internal combustion engine provided with a housing structure that contains two shafts which rotate in opposite directions to each other and at the same rotational velocity. Pairs of counterweights are attached to the two shafts in order to provide a counterbalance force which is generally equal to an opposite from the secondary shaking force which results from the reciprocal movement of the pistons of the engine.